The present invention relates to a crank angle sensor and an ignition timing control system using the crank angle sensor.
JP 47-38658 discloses a crank angle sensor including a slit disk or rotor plate, a source of light, and a photo-electric transducer. The rotor plate is coaxially coupled with a shaft of a distributor rotatable with a crankshaft of an engine. The rotor plate is formed with a first group of slits arranged equi-angularly distant one after another within an outer annular zone adjacent the outer periphery of the disc, a second group of slits arranged equi-angularly distant one after another within an intermediate annular zone coaxially and inwardly disposed next to the outer annular area, and a third group of a slit arranged within an inner annular zone coaxially and inwardly disposed next to the intermediate annular zone. The first group of slits are designed for detecting a crankshaft angle, the second group of slits for detecting a cylinder angular position, and the third group of a slit for detecting an angular position of a specified cylinder. The source of light emits three beams of light on the three annular zones, respectively. As the slit disk rotates, the photo-electric transducer generates a pulse when the light passes through each of slits. Three different trains of pulses are generated corresponding to the three groups of slits, and processed so as to provide timing signals which may be used for an ignition timing control or injection timing control or any other timing control necessary for the engine control.
The rotor plate of this known crank angle sensor is complex and weak in structure and thus difficult to manufacture since three groups of slits are formed in three coaxially arranged zones, resulting in increased manufacturing cost.
U.S. patent application Ser. No. 440,559 filed on Nov. 22, 1989, now pending, discloses a crank angle sensor using a less complicated rotor plate. This rotor plate is formed with two groups of slits. The first group of slits are arranged equi-angularly distant one after another within an annular zone adjacent the outer periphery and designed for detecting a cylinder angular position. The second group of a slit is arranged in the same annular zone and designed for detecting an angular position of a specified cylinder.